Something has to dry out to guarantee the PCB is broken within twenty yearsto provide assurance that new hardware is always marketable.

Electrolytics provide functionality of spontaneously blowing up every once in a while.They also don't mind slowly leaking, causing corrosion of other components (Kamikaze style A).They are also masters of manipulation, and might choose to maintain composure whilemalfunctioning, causing the customer to discard an entire PCB (Kamikaze style B).

Capacitors tackle dc voltage. This is really necessary for a pack of circumstances. You'll use a pack of small power capacitors crossed logic ICs to "de-couple".

Capacitors also "smooth" out waves in charges, that's why a largish capacitor is used in energy supplies - to overcome the "ripple voltage" whatever happens from rectification (using diodes to convert AC to DC.)